A wide variety of cosmetic compositions for application to human skin make use of a thickened or structured liquid carrier to deliver colour or some other active material to the surface of the skin. A significant example of such cosmetic compositions are antiperspirant compositions which are widely used in order to enable their users to avoid or minimise wet patches on their skin, especially in axillary regions.
Antiperspirant formulations have been provided with a range of different product forms. One of these is a so-called "stick" which is usually a bar of an apparently firm solid material held within a dispensing container and which retains its structural integrity and shape whilst being applied. When a portion of the stick is drawn across the skin surface a film of the stick composition is transferred to the skin surface. Although the stick has the appearance of a solid article capable of retaining its own shape for a period of time, the material usually has a structured liquid phase so that a film of the composition is readily transferred from the stick to another surface upon contact.
Another possibility is that a stick is a softer solid composition accommodated in a dispensing container which in use extrudes the composition through one or more apertures.
Antiperspirant sticks can be divided into three categories. Suspension sticks contain a particulate antiperspirant active material suspended in a structured carrier liquid phase. Emulsion sticks normally have a hydrophilic phase containing the antiperspirant active in solution, this phase forming an emulsion with a second, more hydrophobic, liquid phase. The continuous phase of the emulsion is structured. Solution sticks typically have the antiperspirant active dissolved in a structured liquid phase which may be a mixture of water and a water-miscible organic solvent. This classification into suspension, emulsion and solution types can be applied to both firm and soft solid compositions.
Other types of cosmetic composition can also be provided in the form of a stick and again the stick may be a structured solution, emulsion or suspension. Examples of cosmetic compositions which are, or can be, marketed in a stick form are lipsticks, lip salves and eyebrow pencils.
There is substantial literature on the structuring or thickening of cosmetic compositions.
Conventionally, many sticks have been structured using naturally-occurring or synthetic waxy materials. Examples of these include those fatty alcohols which are solid at room temperature, such as stearyl alcohol, and hydrocarbon waxes or silicone waxes. Such materials are widely available, and by suitable selection of the materials themselves and their concentrations in the formulation, it is possible to obtain either a soft solid or a firm solid. Examples of these sticks are described in an article in Cosmetics and Toiletries, 1990, Vol 105, P75-78 and in U.S. Pat. Nos. 5,169,626 and 4,725,432. However, fatty alcohol or wax structured sticks tend to leave visible white deposits on application to human skin, and the deposits can also transfer onto clothing when it comes into contact with the skin and the wearer can, for example, find white marks at the armhole of the sleeveless garment.
Some alternative structurants have been proposed. The term "gellant" is often employed instead of "structurant". Where the resulting product is liquid of increased viscosity rather than a solid or gel, the term "thickener" can also be used. For example, the use of dibenzylidene sorbitol (DBS) or derivatives thereof has been proposed as gellant in a number of publications such as EP-A-512770, WO 92/19222, U.S. Pat. Nos. 4,954,333, 4,822,602 and 4,725,430. Formulations containing such gellants can suffer from a number of disadvantages, including instability in the presence of acidic antiperspirants, and comparatively high processing temperatures needed in the production of sticks.
A combination of an N-acylaminoacid amide and 12-hydroxy stearic acid to gel a non-aqueous formulation is described in, for example, WO 93/23008 and U.S. Pat. No. 5,429,816. However, high processing temperatures are needed to dissolve the gellants and prevent premature gelling. When applied to skin the formulation can be difficult to wash off, but reformulation to overcome that problem can be made impossible by the need for a high processing temperature.
The use of 12-hydroxy stearic acid without N-acylamino acid amide as a secondary gellant has been disclosed in some documents such as Japanese application 05/228915 and U.S. Pat. No. 5,744,130.
In WO 97/11678 to Helene Curtis, Inc, there is described the use of lanosterol as a gellant to make soft gels, sometimes in conjunction with a starch hydrolyzate derivative for antiperspirant compositions. This document includes a brief reference to cellulose as a possible ingredient. Cellulose is of course a polymer.
In WO 98/34588 to Lancaster Group GmbH, there is described the use of lanosterol as a gellant for oil-based cosmetic compositions, containing a cosmetic active material, of which one listed material is a deodorant, though not exemplified.
EP-A-400910 discloses cosmetic compositions in which a powdered form of cellulose is used as an absorbent for liquid material. In one example such a powder is used to absorb volatile silicone and the resulting material is used as a particulate ingredient in a stick which also contains particulate antiperspirant active and a binder polymer.
Antiperspirant emulsion sticks without any material identified as a structurant have been disclosed in U.S. Pat. Nos. 4,673,570, 4,948,578 and 5,587,153.
Cosmetic compositions other than antiperspirants which take the form of structured liquids have been disclosed, for example in U.S. Pat. Nos. 3,969,087, which disclosed the use of N-acylamino acids and derivatives thereof as gelling agents, U.S. Pat. No. 5,486,566 which utilised 12-hydroxy stearic acid.